Fluid handling – Systems – With pump
Patent
1997-09-18
1998-09-15
Michalsky, Gerald A.
Fluid handling
Systems
With pump
60384, F15B 1310
Patent
active
058065610
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic control arrangement having a directional valve, a metering pump unit which has two metering pumps that are connected hydraulically in parallel and operable mechanically in parallel, and a shut-off valve in a hydraulic connection between the two metering pumps, a pump connection and a tank connection which are connected to the metering pump unit by way of the directional valve, and two working connections which are connected to the directional valve, a control inlet of the shut-off valve being connected to the pump connection.
Such a control arrangement is preferred for the steering of vehicles. In that case, the metering pumps and the directional valve are connected to a steering hand wheel or to a similar device. When the steering hand wheel is turned, the directional valve is displaced in the desired direction and the metering pump unit continues to convey hydraulic fluid until a steering motor connected to the working connections has reached the desired position. In normal, undisrupted operation, both metering pumps are active. They can convey an appropriately large volume of hydraulic fluid, which enables the steering motor to react rapidly to movements of the steering hand wheel.
The metering pumps can, however, also be used as auxiliary pumps in so-called "emergency operation", when the pressure at the pump connection falls or fails for whatever reason. In that case, the metering pumps are actually used to produce pressure in the hydraulic fluid. For that purpose, the energy required must be introduced by way of the steering hand wheel, that is to say generally by human muscle power. In order to facilitate the task for the operator, it is known, as disclosed in DE 22 28 531 C2, to provide a shut-off valve, with the aid of which the second metering pump is turned off in the event of a pressure failure at the pump connection. The operator then has to actuate only one metering pump. To achieve the same displacement of the steering motor, he then has to turn the steering hand wheel further. The effort required to do so is, however, smaller.
In normal operation such a system functions in a generally satisfactory manner. Even in emergency operation satisfactory results can be obtained in many cases.
However, disruptions can occur, particularly in emergency operation, that make what is already unpleasant operation still more difficult. For example, the shut-off valve, which turns off the second metering pump in the event of a pressure failure in the pump, may unexpectedly be opened again, that is to say it may make the connection between the two metering pumps, which causes an abrupt increase in the load on the steering hand wheel. There can be various causes for the opening of the valve. For example, there may be a sudden increase in pressure in the corresponding control line as a result of an external influence on the steering motor, as can happen, for example, if the steered wheel in a steered vehicle encounters an obstacle, a so-called "kick-back". In such cases, resistance to turning the steering hand wheel (or to moving the corresponding control means) increases virtually instantaneously, as a result of which not only an unpleasant, but even a health-endangering, impact may be passed on to the operator.
The problem underlying the invention is therefore to design the control arrangement so as to be user-friendly.
SUMMARY OF THE INVENTION
That problem is solved in a control arrangement of the type described at the outset by providing a safety valve arrangement between the control inlet of the shut-off valve and the directional valve.
That safety valve arrangement prevents pressure surges, which, in whatever manner, reach the pump connection-side inlet of the directional valve, from being transmitted to the shut-off valve. Instead they are intercepted by the safety valve arrangement and cannot result in a change in setting of the shut-off valve. Since the safety valve arrangement is arranged between the control inlet of the shut-off val
REFERENCES:
patent: 2134399 (1938-10-01), Dawson
Pedersen Poul Henning Holm
S.o slashed.rensen Ole Vincentz
Danfoss A/S
Michalsky Gerald A.
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